Subject to Revision. 


[TRANSACTIONS OF THE AMERICAN INSTITUTE OF MINING ENGINEERS.] 


THE WHITWELL FIREBRICK HOT-BLAST STOVE , AND 
ITS RECENT IMPROVEMENTS. 

BY F. W, GORDON, PITTSBURGH, PA. 

(Read at the Philadelphia Meeting, February, 1881.) 

The Whitwell firebrick hot-blast stove, for furnace use, may be 
seen in its three main stages of development in the accompanying 
drawings. Fig. 1 is the stove of 18G9, the year in which it was 
thoroughly tested at the Consett furnaces, England; Fig. 2, the 
stove of 1876 and 1877, in which it was intended to reduce the cost 
by increasing the height; Fig. 3, the stove of 1880. Many modifi¬ 
cations were made from time to time, generally in the direction of 
improvement, but the drawings illustrate the main features of 
progress. 

In the stove of 1869 the plan was to introduce the gas at A, 
and pass it up and down between each alternate wall, the air in 
the reverse direction, passing in atB. The friction in this stove was 
so great, owing to the restricted area of the passages and the many 
reversals of the gaseous current, that it was deemed imprudent to 
build the stoves higher than 28', 6". Another reason was that the 
great importance of cleaning was carefully kept in view, and it was 
very difficult to operate any hand scraper even to this depth. For 
these reasons the 22' X 28J' stove held the field for several years. 
A slight change made from this was to the 18' X 40' stove, where 
the height was increased, but the number of walls diminished. In 
this stove the friction was somewhat reduced, but so was the heating 
surface, and although it cost a little less it was not any better. 

The next important change, seen in Fig. 2, was by increasing 
the height to 60 feet and keeping the full number of walls in the 
stove. The heating surface and mass were much increased in propor¬ 
tion to the cost, and the friction decreased by alternating over and 
under two or more walls, instead of one, as formerly. This stove 
gave admirable satisfaction, but, although the proper doors were pro¬ 
vided, it was very difficult to clean, owing to the long distance the 
scrapers had to traverse. 

Stove No. 3 is a modification of No. 2. The great question 

1 


/ (o y >/) 



2 


-TW'V'’ 

WHrTWELL FIREBRICK HOT-BLAST STOVE. / 

was how to decrease the cost without imparing in any way the 
efficiency or durability of the stove? In this plan the gas passes up 
and down the stove twice, as does the blast, but in the reverse 
direction. Thus we have very far departed from the 1869 stove, 
where the ups and downs were five in number. The number 
of walls traversed in this case are five, while the cross or stay-walls 
are eleven, instead of three, as formerly. We have thus increased 
the area of surface very greatly, while the friction of the total stove 
has not been increased, since the speed of the currents has been 
much diminished by increasing the aggregate area of the passages. 

It is a matter of much importance to have this properly propor¬ 
tioned, as it insures: 

1st. The utilization of every foot of surface exposed. 

2d. The prolonged use of the stove without cleaning. 

3d. The forcible contact of the air with every heated brick, and, 

4th. The thorough mixture of the gas and air while heating the 
stove, causing the most perfect combustion. 

If the area for the passage of a limited amount of gas or air were 
indefinitely increased the surface exposed would be but partly util¬ 
ized. We consider that an area so great that the currents are much 
below ten miles an hour too great to be wholly effective. This cur¬ 
rent, ordinarily called a “fresh breeze,” will prevent the deposit of 
the light flocculent material on the walls, so highly detrimental to 
the heating power of the stove. Only heavy solid matter will col¬ 
lect, which must be scraped off'. To this end we provide a swivel crane, 
pivoted in the centre of the stove top. The carriage of this crane can 
be made to operate the chain directly over any of the heating pass¬ 
ages. To this chain is attached a heavy weighted scraper, counter¬ 
balanced on the other end of the crane beams. The scraper can be 
rapidly run up and down the walls even while quite hot. In fact 
the stove can be taken off blast, and work of cleaning immediately 
commenced. The chimney damper being left slightly open,all heat 
will be drawn away from the men at work. 

The speed of gas consequent on thus limiting the area of the pass¬ 
ages does not present any difficulty in the matter of draft. A chimney 
with a head of draft equal to 1 inch of water is all that is necessary, 
and 150'to 175' in height is ample. The entire friction of the stove, 
when on gas for normal duty, does not exceed \ inch of water; in¬ 
deed the friction of the blast, from one end to the other, is only ' s of 
an inch, the valve friction not being taken into consideration. 

You will observe that, though slightly modified, the air channels 


WHIT WELL FIREBRICK HOT-BLAST STOVE. 


3 


for heating the oxidizing air are in the main the same as in the older 
stove. The bricks being fully heated, the air in passing through 
the channels takes up an amount of heat which very materially aids 
the combustion. We might here say, that as blast-furnace gas is 
necessarily much reduced in combustibility, by an admixture of from 
14 to 15 per cent, of C0 2 , it is desirable to use all means to effect a 
thorough combustion. These channels in the wall may be objected 
to as ineffective after the first few moments, but the work of any 
continuous regenerative furnace will fully demonstrate that a very 
great amount of heat can be taken up by air having a brick partition 
between it and the flame. We always insure a sufficient strength in 
the walls after the passages are deducted, and these openings are not, 
therefore, detrimental to the strength of the stove. Another means 
lately introduced to aid the combustion of the gas is to introduce a 
jet of heated air from the stove then on blast, admitting this blast 
through a number of small tuyeres, placed in the bottom of the com¬ 
bustion-chamber. This we have found amazingly effective. 

In the “ ideal working” of the blast furnace, where all the carbon 
is burned at the tuyeres to CO, and all reduction is effected bv the 
oxygen of the ore burning this gas to CO, 2 , 5.7 pounds of air will be 
required for each pound of carbon charged. In this case (were it 
possible) a good grade of ore could be smelted with .506 pound of 
carbon to the pound of iron, actual reduction requiring by the above 
assumed process .312 pound of carbon, and .312 X 8080 = 2521 
calories. The portion of this heat at the tuyeres is .312 X 2473 = 
771.57 calories (C to CO), and .312 X 5607 in zone of reduction (the 
CO to CO,). The total calories required, independent of the heat 
from the blast, being about 3000, there is further required in the zone 
of combustion, 479 calories, which require .194 pound carbon, burned 
to CO. This latter passes away in that condition. The total car¬ 
bon, therefore, consumed from the fuel is .312 + .194 = .506 pound, 
which multiplied by 5.7 pounds gives 2.884 pounds of air to the 
pound of iron. This measure of economy need not be expected to 
be reached until our present mode of reduction can be entirely 
changed. It is however the smallest amount of air possible for a 50 per 
cent, ore, using 25 per cent, of lime. By the aid of the Whitwell 
hotblast this same quality of ore has been through a year’s work 
reduced with .819 pounds of carbon to the pound of iron, which 
required 3.75 pounds of air; the proportion of CO to C0 2 being 
much smaller than in the case assumed. Where, however, an ordi¬ 
nary economy of product with high heats is attained, say 1 pound 


4 WHITWELL FIREBRICK HOT-BLAST STOVE. 

of carbon (1.15 pounds of coke), to the pound of iron, the weight of 
air would scarcely exceed 4.5 pounds. For practice, however, in 
figuring the heating surface of the stoves, we assume 5J pounds of 
air to the pound of iron, and as the air at ordinary atmospheric 
temperatures weighs .076 pounds per cubic foot, 72 cubic feet of air are 
required to make 1 pound of iron; or, allowing 23 hours’ blowing 
for a day’s work, 117 cubic feet of air per minute are required for 
1 ton of iron per day. From actual tests we know that 5 feet of 
surface in the plant of stoves is sufficient for 1 cubic foot of air per 
minute, but allowing 20 per cent, loss in engines, etc. (a fair 
allowance where machinery is good), 4 feet of surface may be pro¬ 
vided in the stoves to 1 of air per minute, counting piston displace¬ 
ment. The surface, therefore, required when good ores are to be 
smelted, will be 117 X 5 = 585 feet per ton of iron per day. 

We must here call attention to a matter of some importance, with 
regard to the Whitwell stoves. If the stoves are to be placed at an 
old furnace, an increased output may be assumed of 70 to 100 per 
cent. The only instances in which this has not been the case is 
where stoves of insufficient capacity have been put up. Where 
ordinary cast-iron pipe stoves have made a product with certain 
ores and fuel, and it is proposed to erect a furnace with Whit¬ 
well stoves thev must be built with a view to this increased out- 

•/ 

put. Thus we expect for a 15-foot coke furnace 100 tons of iron per 
day, or if the ores are especially good a make of 115 tons can be 
reached, and where the ores are lean and silicious 75 tons is all that 
can be expected. We wish to have it well borne in mind that the 
leaner the ore the more air per ton is required, and vice versa , and 
it would be approximately correct to calculate the size of the 
stoves based upon the amount of ore used. Or the following method 
may be used, which avoids the extremes of basing the size of the 
stoves upon the air per minute with the assumption of a fixed quan¬ 
tity per pound, and the percentages of the ores. Multiply the 
number of pounds of ore required per pound of iron by 190, and 
add the constant 220. This will equal the total stove heating sur¬ 
face per ton of iron per 24 hours. This, again, depends upon the 
cubical contents of the blast furnace, since, ordinarily, the leaner 
the ores the less the product; and as the leaner ores require the 
greater amount of air per unit of iron, therefore the greater amount 
of heating surface is required. The American coke practice with 
high heats has reached the production of 1 ton of iron per 24 hours 
to 90 cubic feet of furnace contents with 60 per cent. ores. Then, as 


WHITWELL FIREBRICK HOT-BLAST STOVE. 


5 


above, 190 X If tons of ore to ton of iron = 317 + 220 = 537, 
which divided by 90 = 6, nearly. We use 6.5 as a multiplier; that 
is, we multiply the cubical contents of the furnace by 6J to obtain 
the heating surface of the stoves, and this result will be nearly cor¬ 
rect for any character of ore. For small furnaces this had better be 
somewhat increased, and for larger ones it may be slightly decreased, 
since small furnaces are greater producers per unit of contents. 
We have thus a “ rule of thumb ” for calculating the stove surface 
required. 

Let us here call attention to a bad practice of comparing furnaces 
by the height and the diameter of the bosh. With these two meas¬ 
urements the cubic capacity may be twice as great in one case as 
the other. We have calculated 16-foot and 13-foot furnaces, and 
found them practically alike. The cubical capacity comprises all 
the dimensions, and is a much more reasonable basis of comparison 
tban«any single measurement. A comparison of duty should be 
made by stating how many cubic feet are required to make a ton of 
iron in twenty-four hours. 

In this connection we should explain how so many furnaces have 
been supplied with altogether too little stove power. The English 
furnaces have an average output of one ton of iron per twenty-four 
hours per 250 feet of cubic capacity, the range being from 170 
to 430. Mr. Whitwell, during his lifetime, had control of this 
county’s business, and he did not or would not recognize the economic 
consideration of large output having greater importance here as com¬ 
pared with the English practice. His recommendations, therefore, 
based upon furnace size, were always too small for high heats in 
American practice. Few of the old type stoves, with their limited 
heating surface, had anything like enough power to do the work ex¬ 
pected of them. Thus the stoves were said to do little better than 
the cast iron, as far as make and output were concerned; but none 
who had them ever regretted putting them in since the economy of 
maintainance alone was full recompense for the outlay. Many stove 
plants have now been in use for years, and have not cost a dollar since 
their erection, and not one of them has cost anything of any moment. 

It is often asked, can a furnace afford gas enough to supply these 
stoves and give a heat of 1400° F. to the blast in addition to raising 
the necessary steam ? As this is a vital question I will endeavor 
to answer it satisfactorily. It is no use to save the fuel in the furnace, 
if what is saved must be expended outside, except perhaps a cheaper 
grade might be used under the boilers. Practice has proved that 


6 


WII IT WELL FIREBRICK HOT-BLAST STOVE. 

anv well-appointed furnace, even with good economy of fuel, pro¬ 
duces gas in sufficient quantity and of good enough quality to raise 
all steam required and heat the blast in cast-iron pipes to 900° F. 
For a unit of blast we will assume that the same amount of steam 
is required when either high heats or ordinary heats are used, and 
we will, therefore, only compare the amount of gas necessary to raise 
the blast temperature in the one case to 900°, and in the other to 
1400° F. The gas from a blast furnace working economically may 
be taken to be 

CO a = 17.25 per cent. 

CO =25.25 “ 

N =57.50 “ 

The temperature produced by the combustion of this gas is that due 
to the further oxidation of the CO less the heat absorbed by the C0 2 
and N and air introduced for the combustion. 

• 

Weight of gas to be burned, say,.100. 

Add air required to burn the 25.25 CO to C0 2 . . . 62.6 

Add for air of dilution, ....... 40.4 

203.0 

The temperature, therefore (specific heat, being .24), is 

10.82 x 5600 _ 22430 c _ 2270° F. 

203 X .24 

This disregards the initial temperature of the gas and air. This 203 
is twice the weight of the gas consumed, and as the blast and gas 
are in the proportion of 1 to 1.35 nearly, the amount of heat 
produced bv the combustion of all the gases would be equal to all 
the blast heated to a temperature 1.35 X 2 X 2270° F. = 0129° F. 
If, therefore, all the heat of the gases could be imparted to the air 
only = 14.7 per cent, would be required to heat to 900°. But 
to generate 900° F. in a cast-iron stove with the ordinary degree of 
rapidity the escaping gases must go off at 1200°, that is only 1070° 
of the 2270° can be made available, requiring 31.1 per cent, of the 
gases burned in the ovens instead of 14.7 percent. The heat lost by 
radiation from the walls of the ordinary cast-iron ovens is very great, 
raising the total combustion to nearly 50 per cent, of the gas. 

This same reasoning applied to the Whit well stoves shows that 
~ 22.8° of all the heat of the consumed gases is returned to 
the furnaces, and as the escaping temperature is only 400°, 2270° — 
400 = 1870° F. are available for heating the blast, and 2270 




WHIT WELL FIREBRICK IIOT-BLAST STOVE. 


7 


X 22.8 -7- 1870 = 28 per cent. To this, as before, must be added 
the heat lost by radiation from the stoves which, with their heavy 
walls and the recurring cooling action of the blast, never attains a 
temperature of more than 150° on the average. In fact, the naked 
hand can be held on the casing in many places. It is, therefore, 
fair to assume that the loss by radiation cannot be anything like 
what it is in the ordinary pipe stove, and 35 per cent, of the gas 
will suffice to raise the blast to 1400° F., which is about the amount 
obtained by measuring the gas currents. In any view, however, it 
is clear that less gas is required to raise the temperature in a Whit- 
well stove to 1400° F. than to 900° in the best style of a cast-iron 
pipe stove. 

The above 35 per cent, of the gas will weigh in units of blast 
35 per cent. X 1.35 = .4725, and multiplied by 2 — .945 gives the 
weight of the products of combustion, and as this amount is used in 
two stoves at a time, this quantity (.4725) passes through each. 

The 21' X 60' stove has a heating surface of 29,000 square feet, 
and three of these will have 87,000 square feet, which divided by 
6.5 gives 13,538 cubic feet of furnace capacity. But as in large fur¬ 
naces this may be increased, as above stated, our estimate is for a 
furnace of 15,000 cubic feet capacity or for a product with rich ores 
of 150 tons of iron per day, equal to 100 cubic feet of furnace capacity 
to the ton of iron. According to our figures 150 X 117 = 17,550 
cubic feet of air per minute, and that multiplied by 5 = 87,750 
square feet of surface in the stoves, which nearly tallies with the former 
estimate. Somewhat less air than the above is required for this 
amount of iron when economy of fuel is made the prime object. 

The proportion of the several passages through which the gas and 
air passes in these stoves has been a matter of much study. We will 
call attention to these currents which serve so well to keep the walls 
clear of fine light dirt. In the first passage of the blast the aggre¬ 
gate is 20.8 square feet, and the surface of the openings is 114 feet 
linear. As the friction is proportional to the surface and the square 
of the velocity, we multiply by these factors to get a unit of resist¬ 
ance, so that the entire resistance shall be the least possible, and the 
the mass the greatest possible. Volume of air = 17,750 feet per min¬ 
ute, divided by 20.8 = 853 velocity per minute, or 14'.2 per second, 
14.2' X 114 = 22,988 units of resistance (neglecting the compres¬ 
sion of the air). In the second passage the resistance is 20,310, and 
in the third 18,934, since they are made freer to compensate for the 
expansion of the air by the heat taken up. The last passage or com- 


8 


WHITWELL FIREBRTCK HOT-BLAST STOVE. 

bustion-chamber has an area of 35.5 square feet with only 52 feet ot 
surface linear, measured around its walls, this chamber being espe¬ 
cially designed for the combustion of the gases. It is evident from 
these data that the How of the gas being but one-halt the quantity of 
the air, the up and down movements, subdividing the large heating 
chamber into three parts, cannot be any detriment in causing too 
much friction to the currents; and when we find less than £ inch of 
water as the actual friction in practice, we feel safe in claiming the 
following important advantages derived from this subdivision. 

1. The complete contact of the air and the brick surface. 

2. The burning gas comes in contact with every brick exposed. 

3. The light flocculent material is carried on by the current, and 
is not deposited on the brick walls to prevent them from absorbing 
the heat. 

These stoves have been greatly simplified in construction, being 
built almost entirely of 9-inch ordinary-si zed brick. The shapes 
seen on drawing (Fig. 3) are very simple and easily made, and the 
number needed of each, marked on it, shows how few are required. 
Further, the double passage that we have just referred to enables us 
to use a common cheap grade of firebrick in the up and down pas¬ 
sages next the chimney valve, as the first flush of heat is taken up 
in the combustion-chamber and the first down passage. This effects 
a very considerable saving in the construction of these stoves. The 
arches below are a thorough network of brick and firebrick only, 
and are so short in their span that it is impossible for them to fall 
in. The base of the centre wall is greatly increased in width to com¬ 
pensate for the bricks removed to form the arches across it. These 
arches are numerous and small, and induce a thorough spreading of 
the gas and blast. 

As before mentioned, the product of the furnace is much increased 
by the application of the superheated air, and to show that such is a 
natural sequence we would refer to I. Lowthian Bell’s report of the 
Consett furnaces when the Whitwell stoves maintained a constant 
temperature in the blast of 1324° F.* The furnaces were almost 
identical; the material the same; ore, fuel, and limestone; but one 
was blown with air at 850° F. and the other with air at 1324° F. 
The furnace with the air at 850° F. required 22.75 cwts. of coke 
to make a ton of iron, while the one with air heated to 1324° F. 
made the iron with 18 cwts., a saving of 4.75 cwts. to the ton, or 


* Chemical Phenomena of Iron Smelting, page 101. 




9 


WHITWELL FIREBBICK HOT-BLAST STOVE. 

21.3 per cent., attributable to nothing save the heat of the blast. 
The product was really the same both in quantity and quality, but 
the furnace with 850° air required 5.07 pounds of air to the pound 
of iron, while the other required only 3.75 pounds. The fact 
of the make being the same is easily explained, when it is known 
that the same blowing power was used for both furnaces. The re¬ 
sistance to highly heated air in passing in at the tuyeres being much 
greater than that of the moderately heated, less would therefore en¬ 
ter the same tuyere area. Both these furnaces had a tuyer> area of 
80 square inches, and Weisbach’s formula for resistance wor ld show 
that as 5 pounds entered the one set of tuyeres at a temperature of 
850°, only 3.77 pounds of air would enter the other, all other things 
being equal, which they must have been, since these proportions are 
almost exactly the same as the air received by the furnaces. Had 
the blowing power been independent and the same amount of air 
been injected into each furnace in a given time, the relative produc¬ 
tion would undoubtedly have been 5 for the furnace with super¬ 
heated air to 3.75, for the other, the make rising from 60 tons per 
day to 80. 

This brings us to what may seem to some at first sight rather dif¬ 
ficult to believe, namely, the construction of a furnace plant with 
Whitwell stoves, royalty, and all, costs no more money than when a 
fair plant of cast pipe stoves is put in. A blast furnace for given ma¬ 
terials is large or small according to the product, and to say it is an 
80-ton furnace, a 60-ton, etc., is more to the point than to give any of 
the dimensions. The diameter of bosh, cubic contents, size of engines 
or boilers, are only the details of the whole, whose duty is some un¬ 
certain quantity of pig metal. Taking these English data (and far 
better results can be shown than these), if the same engines, boilers, 
buildings, and furnace proper can be made to produce 80 instead of 
60 tons per day, without being any more tasked, they are unques¬ 
tionably worth 33J per cent, more money. We will assume, there¬ 
fore, for comparison, these parts of a certain furnace to produce a 
stated quantity of iron to cost $100,000, and with the cast-iron 
stoves to cost $120,000. The Whitwell stove plant with chimney and 
fiues will not cost over $50,000, or a total of $150,000. But as this 
latter for actual output is worth one-third more than the former, its 
relative value would be 120,000 -f- 1 - y 00 = $160,000. Or, to take it 
the other way. If the machinery, etc., all regulated by amount of 
air required, could be reduced in the ratio of from 5 to 3.75, and 

2 


10 


WHITWELL FIREBRICK HOT-BEAST STOVE. 


with the aid of the stoves still make the same amount of iron, and 
this saving added to the cost of a east pipe stove plant, there would 
be more than enough money to build a fine plant of Whifcwells. 

The above is by no means our best results. The application of 
the stoves to existing plants has fully doubled the output in several 
instances. Why is this great increase of output the result of the 
application of the Whitwells? By blowing superheated air into 
the furnace a combination of several advantageous points results. 
Less fuel is used per ton, therefore there is more ore in the fur¬ 
nace. Less blast is used, therefore less heat is carried away in the 
gases. The sensible heat of the gases is always lower, and part of 
this loss is prevented. The more highly heated the blast the greater 
affinity its oxygen will have for the incandescent carbon in the 
hearth, therefore the more rapid the formation of the CO ; and the 
more rapid the combustion the more the area of combustion is con¬ 
fined, and the sooner the zone of reduction will be established. The 
more intense the combustion the more limited the zone of fusion, 
the intensity of the heat being greater but the quantity of heat less. 
The work performed where high heats are employed is done quickly 
and well, but the heat is very rapidly reduced to such a point that 
reduction can actively commence and be perfected in a region much 
lower down in the furnace. Thus a low furnace will do the same 
work as a much higher one, and a high one can be proportionately 
pushed, so that in either case a great economy of fuel results. 

The variation in the temperature of the blast from the stove, from 
the time it is first put on tilt taken off, an hour afterwards, is ob¬ 
jected to by some furnacemen. This change is very small with good- 
sized stoves; still we have devised a means of providing against any 
change. The device by which this is effected is based upon the dif¬ 
ference in the resistance to the passage of a certain quantity of air 
at different temperatures. A freely moving piston forms a valve, 
the upper end of which is pressed upon directly by the cold air, arid 
the lower end by the heated column which has passed through the 
stoves, valves, and part of the pipes. If the air is much heated, 
the pressure in this latter pipe is so much less by the extra resistance 
due to that temperature, and the result is a depression of the valve 
by the cold air column, and an admission of cold air to regulate the 
temperature of the blast entering the furnace. When the temperature 
in the stove diminishes the balance of these pressures causes the valve 
to rise and reduce proportionally the amount of cold air. By weight¬ 
ing the lever attached to the valve a constant temperature can be 


WIIITWELL FIREBRICK IIOT-BLAST STOVE. 


11 


maintained at the tuyeres. We are endeavoring to perfect a pyrom¬ 
eter operated by the difference in friction of hot and cool air, and 
thi nk we can succeed. 

It is easy to demonstrate what an immense quantity of heat a 
plant of these stoves contains, and what a small proportion of this 
is taken away by each hour’s run. The only reason there is any 
noticeable difference in the temperature of the blast is, that a slight 
film of surface is more highly heated than the body of the bricks; 
but, the body of the bricks being heated through and through, the 
heat is very slowly taken away, and the surface temperature can be 
well kept up for a very long time when sufficiently large stoves are 
in use, as herein recommended. As already stated, one stove, 
21 feet diameter, and 60 feet high, has a surface of 29,000 square 
feet. This lias 17,550 cubic feet of air passed through it per minute, 
or 1,053,000 per hour, the length of ordinary air-blow. The weight 
of this air is 1,053,000 X .076 = 80,028 pounds, which, multiplied 
by .237 (specific heat) X 1300° F. (less temperature of cold air 
pipe) = 24,654,500 pound-units per hour. As the specific heat of 
firebrick may be taken at .2, and the average thickness of the walls 
6 inches, compared with heating surface (by averaging the 9-inch 
division walls and the small wall crossings), then 29,000 X .2 X 
3-inch (half wall) X 10 (weight of square foot of brick 1 inch thick in 
pounds), we have the units of heat per degree of wall = 174,000. 
But the hour’s blast absorbs 24,654,500 units, requiring a lowering 
of the temperature of 140° F. of the mass of the walls under con¬ 
sideration. This does not, however, represent the diminution of the 
blast temperature, as the greater reduction of temperature in the 
walls is toward the cold end, leaving the heat of the hot end well 
up to the maximum. This reduction, however, is the great safe¬ 
guard to the longevity of the stove. If the gas were admitted con¬ 
tinuously, burning among the heated walls, the temperature would go 
on increasing, as long as a balance could be maintained in its favor 
against radiation and heat of the escaping gases, and the destruction 
of the walls would inevitably result. But in each three hours one 
hour is taken up in carrying away the heat given to this stove during 
the other two, and as a consequence the walls never attain a tempera¬ 
ture that can injure them. Our stoves, therefore, are everlasting. 
This heat, imparted from the walls of the stove and given up to the 
blast, has to traverse through the bricks, an average distance of 1J 
inches, since the wall is 6 inches thick, and acted one on each side. 
(If, as is supposed by some, the walls are only heated and cooled half 


12 


WHITWELL FIREBRICK IIOT-BLAST STOVE. 


an inch, we would ask, where does the heat come from to heat the 
volume of blast, as ordinarily proportioned to the stoves.) Since the 
quantity of heat conducted through solid bodies is inversely propor¬ 
tional to the distance travelled, and directly proportional to the dif¬ 
ference in temperature, and as one inch of firebrick has speed of 
conduction per minute of .33 units to the square foot to each degree 
of Fahrenheit, for 1J inches thick, the amount will be .22 units; and 
since the number of units per minute is 610,910 ■— 29,000 = 21 per 
minute per square foot of surface 21 -r- .22 = 95°, the difference 
between the heat at the surface and the heat at the centre of the 
walls. If the walls were made thinner than 6 inches, the difference 
in temperature would be less; but the total heat of the wall would 
be relatively decreased ; and as the above difference is very slight, 
compared with the entire heat of the mass, this mass should not be 
decreased or sacrificed to heating surface. 

Mr. Whitwell held there was no economy in decreasing the walls 
below 9 inches, claiming that the surface was sufficient to absorb all 
the heat these walls could spare for regular work; but we consider 
that the heating surface cannot be too great if the mass is not sacri¬ 
ficed in getting it. We have adopted the thickness of 4J inches for 
the thin walls, and 9 inches for the dividing walls, as bricks lay 
more cheaply in this shape, and because it is the best, or nearly the 
best, proportion between surface and mass. 

It would, of course, be an easy matter to construct these stoves with 
2-inch walls, and thus, with less brick mass, and the same iron shell 
and valves, obtain perhaps 70 per cent, more heating surface. But, 
from the foregoing considerations, mass seems preferable to surface. 
At least the latter should not be increased at the expense of the 
mass. We think there is sufficient conductivity in firebrick for an 
average thickness of 6 inches, heated and cooled alternately on each 
side, and that the surface so obtained is sufficient to abstract and 
utilize all the heat from the mass to its centre, and thus produce a 
practically uniform temperature in the blast. 

An objection sometimes offered to the use of high heats is, that it 
injures the quality of the iron, and to answer broadly that it does 
not would not be accepted as conclusive. But we can, nevertheless, 
say, witi >ut hesitancy, that far from injuring the iron the quality of 
the iron s improved. The facts bear this out, but we give the fol¬ 
lowing reasons why it should be so. The following materials are 
generally supposed to be detrimental to iron: Phosphorus, sulphur, 
and silicon. The first cannot be removed even in part by any 


13 


WHITWELL FIREBRICK HOT-BLAST STOVE. 

known processes in the blast furnace. The second may, by heavy 
liming, be carried into the slag to a great extent, if it is not volatil- 
lized in the upper part of the furnace; but it is generally recog¬ 
nized that high or low heat in the blast has little or nothing to do 
with the presence of sulphur in the pig. It has been generally sup¬ 
posed, however, that high temperature increases the amount of silicon 
in the pig. This belief grew out of the contrast of cold-blast and 
hot-blast charcoal iron, the former having about J per cent, and the 
latter from 2 to 2J per cent, as ordinarily made in the old-style 
charcoal furnace process. But the tact is in neither case should 
there be more than the smaller amount of silicon in the pig with 
charcoal for fuel. 

All the silica can be fluxed with a proper admixture of lime be¬ 
fore its reduction can take place, except that portion which is covered 
and protected by the carbon of the fuel, that is to say, the silica of 
of the ash. This ash it is which causes the trouble in all light, weak, 
and highly siliconized irons. When fuel high in ash is charged into 
the furnace do not blame the furnace manager, for he cannot make 
strong iron ; but if your fuel ash is low, and the iron weak, increase 
the burden or lime, or both, as there is no other .trouble. High tem¬ 
perature of the blast intensifies the heat of the hearth but only in a 
very slight degree, but it promotes economy of fuel to a very marked 
degree. It also reduces proportionally the consumption of the fuel in 
the hearth, since all the carbon deposition in the reducing zone will 
expose to the action of the flux the ash which was contained in that 
portion of the fuel. If all the ash of an average coke were to descend 
to the tuyeres, and 1J tons of coke were used fora ton of iron, the iron 
might contain from 6 to 7 per cent, of silicon, but by using high 
heats the coke can be reduct'd to one ton and a large proportion of 
the carbon and ash separated in the preparatory action of the furnace. 

DISCUSSION. 

Mr. Birkinbine : Mr. President: Do I understand the gentle¬ 
man to claim that with two furnaces of equal size and proportions, 
similarly equipped, using the same ore, flux and fuel, and operated 
under the same management; in fact, alike in all respects, except that 
one was supplied with Whitwell stoves, while the other used good 
iron pipe stoves that the one equipped with \\ hitwell stoves would 
produce 60 to 70 per cent, more pig iron than the furnace having 
iron pipe stoves and show corresponding reduction in fuel consump¬ 
tion ? 


14 


WHIT WELL FIREBRICK IIOT-BLAST STOVE. 

Mr. Gordon: That is what I intended to say and it can he 
verified. 

Mr. Birkinbine: I regret that I was not aware of the purport 
of this paper, so that I might have come prepared with actual data 
for which under the circumstances I must trust to memory. But J 
do not feel that we should allow the statement that the use of the 
Whit well stoves will augment the product of a given plant GO to 
70 per cent, to pass unchallenged. To no one person do the blast¬ 
furnace managers owe more than to the late Thomas Whitwell, for 
it was he who taught us the true value of a hot-blast in controlling 
the operations of a blast-furnace. Up to the time his stoves were 
presented for public consideration, our furnace managers had treated 
the hot-blast stoves more as an accessory to the plant than as an 
essential feature with which to control and operate it, but I submit 
that the claims made for the superiority of the Whitwell stoves have 
not been substantiated in American practice. In a paper presented 
at the Washington meeting five years ago, I claimed that, if the 
same amount of study and attention was devoted to the construction 
of iron pipe stoves as is bestowed upon the Whitwell plants, and if 
an equal amount of care were exercised in watching the iron pipe 
stoves as is demanded for the firebrick stoves, the claim for superior 
durability would have little foundation. You, Mr. President and 
many of the gentlemen now present, are well aware that it lias been 
the too prevalent practice to allow an iron pipe stove to care for 
itself. An occasional inspection to see that the gas was burning, 
was considered sufficient, and the pipes were subject to sudden 
changes of temperature by throwing open the doors when the oven 
was considered too hot, or when the furnace was blowing out, causing 
the pipes to check and crack. It has not come within my experience 
to find many burned pipes, although 1 have examined a large num¬ 
ber which have been removed from ovens. The cracks indicate that 
they are damaged or destroyed by sudden or extreme changes of 
tern perature. 

As to the durability of iron pipe stoves, permit me to cite an 
example or two. About two months ago I inspected an iron pipe 
stove which had been constructed in 1860 and had been in almost 
constant use, and the proprietor informed me that during these twenty 
years of use not a pipe or brick had been removed from this oven. 
I am at present rebuilding the firebrick arches of the combustion 
chambers of an iron pipe stove. These arches were cut in ridges by 
the gases, the brick cindered, and 15 inches of this cinder had accu- 


WHITWELL FIREBRICK HOT-BLAST STOVE. 


15 


inulated on the bottom of the chambers, yet we have not discovered 
a single defective pipe although they were placed just above these 
chambers which show the action of the intense heat so strongly. 
Other instances of durability could be mentioned if time would per¬ 
mit. 

Concerning the fuel economy I cannot speak as definitely on the 
coke practice as on that of the anthracite furnaces, but while in 
Pittsburgh I found that the work done at the Eliza and Soho fur¬ 
naces with iron pipe stoves compared very favorably when size of 
furnace, quality of stock, and product were considered, with other 
furnaces using the Whit well stoves. 

As to the results with anthracite furnaces I know that to-day the 
Cedar Point furnace at Port Henry, N. Y., 17 feet X 71 feet, not¬ 
withstanding it has 4 Whitwell stoves under efficient management, 
is not making as much pig iron, nor working on as low fuel con¬ 
sumption as the Warwick furnace which is smaller, 15 X 55, and 
uses leaner ores. During our Wilkesbarre meeting in 1877 an op¬ 
portunity was given to compare the contemporaneous working of the 
Port Henry and Scranton furnaces using the same ore and coal, and 
the statements which Were then offered for examination showed no 
perceptible difference between the furnace employing superheated 
blast and blast at 800° from iron pipe stoves. 

These facts are presented as they occur to me now in this crude 
manner. I would not be considered as detracting from the value of 
any improvement in blast-furnace construction or operation. I have 
no financial or personal interest in any form of hot-blast stove, and 
have no pet theories, but I insist that within our present knowledge, 
the firebrick stoves have not developed the economy of fuel claimed for 
them, and I very much doubt if Mr. Gordon can name any three 
furnaces having Whitwell stoves which use anthracite coal, or an¬ 
thracite with a small mixture of coke, which can show a record 
either as to amount of iron produced or economy of fuel consump¬ 
tion, which will not compare unfavorably with the work now being 
done at the furnace of the Pottstown Iron Company, managed by our 
member, Mr. Janney ; the Warwick furnace managed by our mem¬ 
ber, Mr. Cook ; and the North Lebanon furnace operated by our 
member, Mr. Brock. The mixture of ores at the first two named 
furnaces run from 38 to 42 per cent., and at the latter plant all 
Cornwall ore is used, which is highly sulphurous, and averages less 
than 50 per cent.; and all three have iron pipe stoves. 































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